The present invention relates to intraocular lenses (IOLs). More particularly, the present invention relates to IOLs that provide accommodating movement in the eye.
The human visual system includes the eyes, the extraocular muscles which control eye position within the eye socket, the optic and other nerves that connect the eyes to the brain, and particular areas of the brain that are in neural communication with the eyes. Each eye forms an image upon a vast array of light sensitive photoreceptors of the retina. The cornea is the primary refracting surface which admits light through the anterior part of the outer surface of the eye. The iris contains muscles which alter the size of the entrance port of the eye, or pupil. The crystalline lens has a variable shape within the capsular bag, under the indirect control of the ciliary muscle. Having a refractive index higher than the surrounding media, the crystalline lens gives the eye a variable focal length, allowing accommodation to objects at varying distances from the eye.
Much of the remainder of the eye is filled with fluids and materials under pressure which help the eye maintain its shape. For example, the aqueous humor fills the anterior chamber between the cornea and the iris, and the vitreous humor fills the majority of the volume of the eye in the vitreous chamber behind the lens. The crystalline lens is contained within a third chamber of the eye, the posterior chamber, which is positioned between the anterior and vitreous chambers.
The human eye is susceptible to numerous disorders and diseases, a number of which attack the crystalline lens. For example, cataracts mar vision through cloudy or opaque discoloration of the lens of the eye. Cataracts often result in partial or complete blindness. If this is the case, the crystalline lens can be removed and replaced with an intraocular lens, or IOL.
While restoring vision, conventional IOLs have limited ability for accommodation (i.e., the focusing on near objects). This condition is known as presbyopia. To overcome presbyopia of an IOL, a patient may be prescribed eyeglasses. Alternative attempts in the art to overcome presbyopia focus on providing IOLs with accommodation ability. Accommodation may be accomplished by either changing the shape of the IOL, e.g., to become more convex to focus on near objects, or by moving the IOL along its optical axis. Examples of this latter approach are disclosed in Gwon et al. U.S. Pat. No. 6,176,878 and Laguette et al. U.S. Pat. No. 6,406,494. The disclosures of both these patents are incorporated herein in their entirety by reference.
In a healthy eye, accommodation is achieved through the actions of the ciliary muscles as well as through changes in the pressure exerted by vitreous fluids on the capsular bag. Prior art accommodating IOLs have typically attempted to take advantage of one of these two naturally occurring mechanisms. For instance, one class of accommodating IOL takes advantage of changes in the pressure of the vitreous fluids by placing the optic of the IOL in direct contact with the posterior wall of the capsular bag. Thus, axial forces on the capsular bag are transmitted directly to the optic. Another class of accommodating IOL takes advantage of the actions of the ciliary muscles by circumscribing the optic with a flexible, anteriorly vaulted movement assembly that converts radial forces on the capsular bag into axial movement of the optic.
IOLs which use primarily only one of these two naturally occurring mechanisms have a tendency to provide insufficient forward axial movement to achieve full range accommodation.
In addition, some of the prior art accommodating IOL designs include relatively stiff outer rings for supporting the IOL in the capsular bag of the eye. These outer rings add stability to the design. However, research has shown that in some designs, the ring may buckle or bend when the capsular bag is compressed. Unfortunately, the buckling or bending does not occur in a predictable or reliable fashion. In other words, a ring may buckle in one location at one time, and in another location another time. Because of this, the compression and movement characteristics of the IOL are inconsistent, and tilting and other undesirable outcomes may occur.
In view of the foregoing, it would be beneficial in the art, and there continues to be a need, to provide new IOLs adapted for sufficient accommodation to overcome or significantly reduce the effects of presbyopia.